Typically, a military aircraft wheel and associated brake assembly are designed for a quick and easy removal from the axle upon which the wheel and the brake assembly are mounted. Initially, the brake assembly should remain on the axle while the wheel is being removed and, thus, prevent an accident if the brake assembly is permitted to slide off the axle with the wheel. Although the brake assembly can remain in an operational position for minor maintenance on the axle after removal of the wheel, typically the brake assembly is also designed for quick and easy removal from the axle.
FIG. 1 is a cross-sectional view of an example of a known aircraft brake assembly 10 and wheel 12. The wheel 12 is received upon a stationary member or axle 13 of an aircraft (not shown) by roller bearing assemblies 14 and 16. The axle 13 includes an axle flange 13A having axle flange openings 13B. An inner cone 15 of the bearing 14 abuts a bushing assembly 17 of a torque tube 20. An axle nut assembly 18 includes a washer 19, which abuts the roller bearing assembly 16. The torque tube 20 includes a plurality of splines 21, a plurality of bolted-on axial extensions 22 received in the axle flange openings 13B, and a torque tube foot 25 in which is located the bushing assembly 17. The bolted-on axial extensions 22 are received in the axle flange openings 13B to prevent rotation of the torque tube 20 relative to the axle 13. As is well known by those of ordinary skill in the art, the torque tube 20 is connected by a plurality of bolts (not shown) to a piston housing 30 of the brake assembly 10. The piston housing 30 includes a plurality of circumferentially spaced-apart piston assemblies 31. The brake assembly 10 further includes a set of stator discs 34 engaging the splines 21 of the torque tube 25, and a set of rotor discs 36 engaging drive keys (not shown) at the wheel 12.
As can be readily seen in FIG. 1, the axle nut assembly 18 retains the aircraft brake assembly 10 and the wheel 12 on the axle 13, by engaging the roller bearing assembly 16 that engages the wheel 12, the wheel 12 engaging the roller bearing assembly 14, the roller bearing assembly 14 engaging the bushing assembly 17 and the torque tube foot 25, which engage the axle flange 13A.
FIG. 2 is a cross-sectional view of a known manually-operated retention mechanism 40 of the brake assembly 10 in FIG. 1. The piston housing 30 (see FIG. 1) includes an outer boss 37 having a radial opening 33, and an inner boss 39 with an opening 38. The outer boss 37 has an outer radial surface 37A. The retention mechanism 40 includes a pin assembly 41 having an enlarged head 42 extending into a shaft 43 having an end part 50 that includes a flange 52. A spring 60 is located about the shaft 43 and trapped between the outer boss 37 and the flange 52 of the end part 50. End part 50 of the pin assembly 41 abuts the flange 13A of the axle 13, whereby the axle flange 13A is trapped axially between the end part 50 and the torque tube foot 25. The retention mechanism 40 requires manual operation so that the aircraft brake assembly 10 (see FIG. 1) may be either mounted upon or removed from the axle 13 of the aircraft. To retract the retention mechanism 40, the enlarged head 42 of the pin assembly 41 must be grasped and pulled radially outwardly in the direction of arrow 62 in FIG. 2, and then rotated so that the enlarged head 42 will engage the outer radial surface 37A when released (illustrated in phantom in FIG. 2). Then, the aircraft brake assembly 10 may be either placed upon the axle 13 or, if already on the axle, removed from axle. If being placed upon the axle 13, the brake assembly 10 will be moved axially along the axle 13 until the torque tube foot 25 abuts the axle flange 13A. The enlarged head 42 is then grasped manually, rotated to the position illustrated in solid line in FIG. 2, and released so that the end part 50 engages the axle flange 13A to couple the brake assembly 10 to the axle 13. Because the retention mechanism 40 is located on the inboard side of the aircraft brake assembly 10, in some circumstances maintenance personnel must be able to locate and operate the retention mechanism 40 without being able to see the retention mechanism.
FIG. 3 is a perspective view of another known aircraft wheel 112 and brake assembly 110 having a manually-operated retention mechanism 140 on the aircraft brake assembly 110. The retention mechanism 140 is illustrated in greater detail in FIGS. 3A and 4. The brake assembly 110 is mounted on an axle 113 of an aircraft landing gear 116. A piston housing 130 of the brake assembly 110 includes a torque take-out extension 133 having a pocket 135 that receives an axle extension 114 of the axle 113. Axle extension 114 includes an extension surface 115. The retention mechanism 140 is mounted, by bolts 141, to the torque take-out extension 133. As can be seen in FIGS. 3A and 4, the retention mechanism 140 includes a pin member 142 received in a lateral opening 152 of a retention bracket 150. A spring 160 is positioned on the pin member 142, and a spring end 164 abuts an outer surface 155 of the retention bracket 150. The pin member 142 has a lever 143, a washer 144 attached to the pin member 142 by a cotter pin 145 and engaging an end 162 of the spring 160, a roll pin 147 located within a portion of the lateral opening 152 of the retention member 150, and a pin member end 148 positioned near a side 157 of the retention bracket 150. The lateral opening 152 of the bracket 150 is a U-shaped through-opening having branches 153 and 154 which may receive the roll pin 147 when the pin member 142 is rotated. As illustrated in FIG. 3A, when the brake assembly 110 is in an operational position on axle 113, the pin member 142 extends through the retention bracket 150 so that the spring 160 is compressed. The roll pin 147 is received in the branch 154 of the opening 152 (not viewable in FIG. 3A). In this position, the pin member end 148 abuts the extension surface 115 of the axle extension 114, thereby retaining the brake assembly 110 on the axle 113. When the brake assembly 110 is to be removed from the axle 113, maintenance personnel must reach around the end of the brake assembly 110, grasp the lever 143 and rotate the pin member 142 so that the roll pin 147 exits the branch 154 whereby the force of the spring 160 causes the pin member 142 to move laterally through the lateral opening 152 until the roll pin 147 abuts an end of the lateral opening 152 adjacent branch 153 (see FIG. 4).
As shown in FIG. 3, the retention mechanism 140 is located on the inboard side of the aircraft brake assembly 110 and, thus, maintenance personnel must be able to locate and operate, without being able to see, the retention mechanism 140. Both lateral and rotational movements of the lever 143 must be accomplished by personnel so that the brake assembly 110 can be either mounted upon or removed from the axle 113. Thus, the operation of the pin assembly 140 is not intuitive to personnel who cannot see the pin assembly. When a maintenance person grasps the pin member 142, his clothing may be snagged or damaged by the cotter pin 145. Additionally, while the brake assembly 110 is mounted upon axle 113, it is possible for the pin member 142 to be hit or damaged by foreign objects and moved to a released position whereby the pin member end 148 no longer abuts the extension surface 115 of the axle extension 114. If the retention mechanism 140 is in the released position when the wheel 112 is removed from the axle 113, the brake assembly 110 can move with the wheel 112 and accidentally come off of the axle 113.